1. Field of the Disclosure
The present disclosure relates generally to a communication system, and more particularly, to selecting between a voice service over adaptive multi-user channels on one slot (VAMOS) receiver and a non-VAMOS receiver in a user equipment (UE).
2. Description of the Related Art
VAMOS is a feature introduced by 3rd Generation Partnership Project (3GPP) to efficiently utilize an available spectrum by multiplexing (or pairing) two voice users in the same radio frequency channels and time slots. In VAMOS, multiplexed (or paired) users are assigned different transmit powers and allocated on either of the quadrature sub-channels. Specifically, in an uplink (UL), VAMOS constructs a multiple-input system, which is typically formed by two UEs. A base station receives signals from both of the UEs within the same radio frequency (RF) (i.e., same frequency and time slot) and is able to differentiate the signals through post processing receiver capabilities. In a downlink (DL), multiple user's data is received with higher-order modulation mode, and each UE identifies its own signal in a specific way.
In conventional systems and methods, the base station can pair and un-pair the UEs from VAMOS without any signaling. The conventional systems and methods do not have an explicit signaling operation in the DL signal for the UE to know about modulation of the downlink signal, i.e., whether it is a Gaussian minimum shift keying (GMSK) signal (i.e., non-VAMOS signal) or alpha-quadrature phase shift keying (AQPSK) signal (i.e., VAMOS signal).
Further, even in VAMOS, during a discontinuous transmission (DTX) period in the DL for the paired user, the DL modulation for the desired user may fall back to the GMSK without any signaling, which decreases receiver performance.
Additionally, the conventional systems and methods utilize a sub-channel power imbalance ratio (SCPIR), i.e., a ratio of a desired user power to a paired user power, in order to identify the modulation of the DL signal. However, the SCPIR is not signaled in the DL signal. Further, the pairing and un-pairing of the UEs can be performed by the base station at any time, without signaling to the UE. Accordingly, it is important for the UE to seamlessly switch between a GMSK receiver and a VAMOS receiver, which negatively affects performance of the receiver in the UE.